The Gut Microbiome and Irritable Bowel Syndrome: How Nutrition Support Can Help

By Megan Gerrard

What is Irritable Bowel Syndrome (IBS)?

IBS is a common digestive condition affecting 1 in 10 people worldwide. Common symptoms include abdominal pain, bloating, and changes in bowel habits. It is recognised as a gut-brain disorder and is often linked to stress, anxiety, and depression. New research suggests that the gut microbiome can play a significant role in the development and perpetuation of IBS. Therefore, understanding its function and how we can support a healthy gut microbiome is crucial for alleviating symptoms. 

The Gut Microbiome and its Role in IBS

Our gastrointestinal tract (gut) is home to the trillions of microorganisms collectively called the gut microbiome. These microbes maintain a mutual relationship with the host and modulate many biological processes, including digestion, regulating our metabolism, and supporting our immune system. A healthy gut microbiome is essential for maintaining overall health and well-being. Imbalances in our gut microbiome, known as dysbiosis, have been linked to IBS and many other health conditions. Findings link distinct microbiome profiles to different subtypes of IBS, including IBS-C (constipation-predominant), IBS-D (diarrhoea predominant), or IBS-M (mixed bowel habits), with further subtypes emerging in the research.

The Multifactorial Development of IBS

The development of IBS involves an interplay between the nervous, immune, and endocrine systems, as well as microbial abnormalities. A few of the many factors which may drive its development include:

• Functional Imbalances; gut dysbiosis, low-grade inflammation, infections and parasites
• Lifestyle Factors; stress, physical inactivity, poor sleep
• Dietary and Nutritional Factors; low fiber intake, food sensitivities, vitamin D deficiency

These factors can lead to changes in an individual’s gut microbiome and increased gut permeability (“leaky gut”) which drives inflammation and disruptions in the gut-brain axis.

The Gut-Brain Axis

The gut-brain axis is the bidirectional communication network between the brain and the digestive system via the nervous system. The enteric nervous system is the nervous system in our gut, which controls gut sensitivity and muscle contractions to move food along the digestive tract. Signalling molecules produced by the gut microbiota are sent back and forth between the gut and the brain. Inflammatory signals from the gut microbiota in the presence of gut dysbiosis and chronic low-grade inflammation can lead to nervous system dysregulation. Similarly, stress signals from the brain can change the composition of the gut microbiome and lead to alterations in the nervous system.

The Hypothalamic-Pituitary-Adrenal (HPA) axis is responsible for regulating the body’s response to stress and is a key part of the gut-brain axis. It connects the gut with the nervous and endocrine systems. Imbalances in the gut microbiota put increased stress on the HPA axis and can lead to dysregulated cortisol release. The subsequent increase of cortisol levels in the body promotes gastrointestinal dysfunction by modulating microbial composition, intestinal immune cell activity, and gut function.

The Gut-Immune Connection in IBS

The gut microbiota are intricately connected with the immune system. The gastrointestinal tract is covered by a mucosal layer, which is where the immune system resides and interacts with the enteric nervous system. Nerve cells sense and mediate the transmission of pain signals to the brain. Changes to the local immune environment as a result of dysbiosis can alter nerve cell sensitivity, which can lead to long-term aberrant pain perception and abdominal symptoms.

How Working with a Nutrition Practitioner Can Help

The causes of IBS are complex and varied, making it challenging to manage alone. Recent advances in our understanding of the gut microbiome enable nutrition practitioners to focus on symptom management through diet and lifestyle, and also interventions aimed at restoring a healthy gut microbiome. They can also help you to understand the drivers and triggers that are unique to you, giving you the tools to manage your symptoms in the long term.